Acid treatment of wells



July 5, 1938- c. E. CLASQN 2,122,452

A'C'ID TREATMENT 0F WELLS Filed Dec. 7. 1956 INVEN TOR.

C. E. C/ason.

ATTORNEY Patented July 5, 1938 PATENT OFFICE ACID TREATMENT 0F WELLS Charles E. Clason, Wichita, Kans., assignor to Halliburton Oil Well Cementing Company,

Duncan, Okla.

Application December 7, 1936, Serial No. 114,586

3Claims.

I'his invention relates to the acidizing off oil wells and more particularly to means and methods for treating separated earth formations with acid.

In the acidizing' of oil wells it often happens that two or more layers of oil-bearing formations are separated by some rock or sand which does not bear oil. If all of these strata are treated with acid undesirable results are obtained, in that the non-bearing formation is rendered porous with the oil-bearing formation, and this often results in water being mixed with the oil or otherwise interfering with the desired increased production of the well.

It is an object of the present invention to provide novel means `and methods for treating the formation of an oil well in such a way that only the desired portions thereof are rendered more porous or subjected to the action of the reagents.

It is another object of the invention to devise novel means and methods for plugging one oilbearing formation while another adjacent thereto is subjected to acid or other reagent.

Other objects and advantages reside in certain novel features of the reagents and methods used, as will beapparent from the following description taken in connection with the accompanying drawing, in which:

The single figure is a diagram representing a. vertical cross-section of the earth and showing an oil well with two oil-bearing formations therein.

Referring to the drawing in detail, it will be seen that an oil well is there shown as comprising a bore hole II having a casing I2 therein and a tubing I3. The casing may be cemented in position, the cement being designated I4.

Beneath the lower end of the casing the well bore may extend into oil-bearing formation. This portion of the bore is designated I5 and is shown passing downwardly through an upper oil-bearing formation I8, a non-bearing formation I'I and a lower oil-bearing formation I8.

Assuming that it is desired to treat both the upper formation I6 and the lower formation I8 without causing acid or other reagent to attack the intermediate formation I'IV the following method or process may be adopted:

'I'he entire well bore, including the casing I2 and the tubing I3, is first filled with oil or other substantially non-compressible fluid. This 'oil is indicated in the casing I2 at I9.

Acid, as for example hydrochloric acid, is then pumped into the tubing I3 by means of a pump not shown, and is forced downwardly through the tubing I3. During this step the casing head at the top of the well is opened to allow the oil to flow ahead of the acid downwardly through the tubing and upwardly through the casing. This step continues until the acid reaches the 5 lower end of the tubing I3. The casing head is then closed and the pumping continued, thus forcing the acid into the lower formation Il. This action taires place because the acid, upon entering the portion I5 of the well bore which is illled with oil, sinks under the action of gravity tothe bottom of this bore and is accordingly forced under the pressure of the pump and the hydro-static column of liquid into the formation. It is also to be noted that the acid enters slightly below the producing formation I6. The oil above the lower end of the pipe I3 prevents the entrance of acidinto the formation IB at this time. To assist the acid in entering the oil properly, the lower end of the tubing I3 is preferably provided with a perforated section at the bottom, as shown at I la, the lower end of this section being plugged.

After sumcient acid has been forced into the formation I8 in this manner, as diagrammatically illustrated at 2l, a quantity of soap solution is forced into the lower formation I8, as diagrammatically illustrated at 2I It will be apparent that if the formation I8 is calcareous in nature the hydrochloric acid sup- 30 plied therethrough will soon react with -the formation and produce a salt, as for example calcium chloride. As soon as the soap solution represented at 2l contacts with the calcium chloride in the formation I8 a precipitate will form, thus forming a. temporary plug. In addition to the calcium chloride or other salt formed in the formation, however, it is desirable to add an additional quantity of calcium chloride to the portion I5 of the bore hole. this being diagrammatically represented at 22.

The quantity of calcium chloride added should be sufficient to flll the lower portion of the well bore up to a point just below the upper oilbearing formation I8. In this way any subsequent acid forced through the tubing I3 will not come in contact with the formation I 1 or the formation I8, these being blanketed olf by the solution 22 which is held in position by the plug formed by the precipitate resulting from the reaction of the soap solution with the calcium chloride.

If now an additional quantity of acid is forced downwardly through the tubing Il it will flow into the upper formation I 6. This body of acid Y' fluids may be removed from the well by pumping,-

swabbing or the like. It is to be noted that as soon as the pressure in the well bore is reduced the oil in the formations I6 and I8 will tend to flow into the well. In so doing, the oil will react with the calcium salts which constitute the precipitate of the soap with the calcium chloride to dissolve the same and thus remove the temporary plug 2|.

The arrangement is such that the blanketing solution 22 may be of a low specific gravity and if desired water may be used for the blanketing solution in as much as there will be little tendency for the body of acid 23 to ow downwardly therethrough. It is desirable, however, to use calcium chloride since this reacts with the soap solution to form a more eifective plug by precipitation. Regardless of what Vfluid is used for the blanket, it cannot travel into the lower formation I8 because of the presence of the plug 2| and merely remains stagnant during the treating of theupper formation I8.

It is of course within the purview of the invention to employ other than hydrochloric acid or to use hydrochloric acid which has been treated to increase its penetrating power into the formation, as disclosedrin the co-pending application of Paul Menaul, Serial No. 96,457, filed August 17, 1936, for Treatment of wells, and it is also within the purview of the invention to protect the metal parts in the well during the acidizing thereof by some electrical means as, for example, that described in the co-pending application of Paul Menaul, Serial No. 77,945, filed May 5, 1936, for Method and apparatus for handling acidic solutions.

Itis known that certain soap solutions combine with calcium chloride to form precipitates and that such precipitates may be used in treating an oil well to separate oil-bearing formations from water-bearing formations. This is disclosed in the patent to Vietti, No. 2,024,119. The present invention is not concerned with permanently separating oilfrom water-bearing formations but with the provision of a temporary spacing blanketing solution between two or more oil-bearing formations. Various soap solutions may be used in accordance with the invention l so long as the precipitate formed is readily. soluble in crude oil.

While only one embodiment and/or method of practicing the invention has been described herein, it is obvious that various changes may be made without departing from the spirit of the invention or the scope of the annexed claims.

I claim:

1. The method of treating wells having separated formations bearing oil or the like which includes the steps 'of first treating the lower formation with an agent capable of reacting therewith to form a salt, then eiectively but temporarily plugging said lower formation by supplying a substance thereto capable of forming an oil soluble precipitate with said salt, adding additional salt solution to the well above the plug so formed to fill the well up to a level near the next higher oil-bearing formation, treating the said higher formation o with an agent capable of reacting therewith, dissolving the plug by bringing oil in contact with the precipitate thereof and removing the resultant fluids from the well.

2. The method of treating wells having `separated basic formati/ons bearing oil or the like which includes the steps of treating the lower formation with-an acid to form a salt, supplying a soap solution to the lower formation to cause the forming therein of an oil soluble precipitate as the result of the reaction with said salt, adding additional salt solution to cause further reaction with the soap solution and additional precipitate and at the same time form a blanket between the lower formation and the next higher oil-bearing formation, treating the upper formation with acid, dissolving the precipitaterin the lower formation by supplying oil thereto and removing the resultant fluids from the well.

mation with hydrochloric acid by using the plug formed in the first mentioned formation as an aid in localizing the body of acid in the desired formation, dissolving the plug by supplying oil to the first mentioned formation and removing the resultant uids from the well.

C. E. CLASON. 

